Plastic lenses are used for mobile phones, digital cameras, vehicle-mounted cameras, and the like, and are required to have excellent optical characteristics suitable for the purpose of the device. Plastic lenses are also required to have high durability including, for example, heat resistance and weather resistance, and high productivity that allows them to be molded at good yield, according to the form of use. Transparent resins such as polycarbonate resins, cycloolefin polymers, and methacrylic resins, for example, have been used as such resin materials.
For achieving a reduction in mounting costs, methods for mounting camera modules collectively by solder reflow have been recently proposed, and plastic lens materials used therefor that can withstand a high-temperature thermal history (for example, 260° C.) in the solder reflow step have been demanded. Conventional plastic lenses, however, have low heat resistance, and are difficult to adapt to the reflow process satisfactorily.
Moreover, a plurality of lenses are used for a high-resolution camera module, in which one of the lenses is required to be an optical material with high refractive index that serves as a wavelength correction lens. Furthermore, in order to improve the yield or production efficiency for manufacturing resin lenses, the molding process is shifting from injection molding that uses thermoplastic resins to press molding that uses curable resins liquid at room temperature.
As disclosed in Patent Document 1, however, most of the conventional materials proposed as materials featuring high refractive index only have improved heat resistance to temperatures not higher than 200° C., and have failed to ensure heat resistance to withstand the solder reflow step at 260° C., for example.
Meanwhile, since satisfactory reflow heat resistance cannot be readily achieved by using organic materials alone, materials provided with heat resistance by mixing organic materials with inorganic particles such as silica have been proposed (see Patent Document 2, for example). In these materials, however, the silica content needs to be increased to achieve satisfactory heat resistance, which has the drawback of precluding an increase in the refractive index of the composition. Moreover, these materials are poor in reliability, because they may have decreased transparency due to the aggregation of the inorganic particles, or may result in brittleness in cured products due to the addition of the particles.